FR2608151A1 - Process for the manufacture of 2-methylbutyryl fluoride - Google Patents

Abstract

Catalytic process for the manufacture of 2-methylbutyryl fluoride from carbon monoxide, hydrogen fluoride and a flow of aliphatic hydrocarbons comprising butane as the main component. It comprises the following sequence of stages: (a) introduction of at least one fluid chosen from carbon monoxide and the said hydrocarbon flow into a reactor in the presence of a super acid consisting of hydrogen fluoride, antimony pentafluoride SbF5 and at least one compound chosen from bromine and inorganic or organic bromides, (b) if appropriate, if it has not already been introduced during stage (a), introduction into the reactor of a fluid chosen from carbon monoxide and the said hydrocarbon flow, under conditions suitable for making possible the formation, as main component, of a complex consisting of the 2-methylbutyryl cation and of the SbF6<-> anion, (c) conversion of the said complex to 2-methylbutyryl fluoride, (d) separation of the 2-methylbutyryl fluoride, and (e) recovery of the super acid. Application to the synthesis of 2-methylbutyric acid.

Description

METHOD OF MANUFACTURING 2-METHYL-BUTYRYL FLUORIDE.

The present invention relates to the field of carbonylation of alkanes in a superacid medium.

It is already known by H. HOGEVEEN and C.F.ROOBEEK, Rec. Trav. Cnim.

Netherlands, 91 (1972) pages 137-140, to react at 00C an equimolar mixture of butane and carbon monoxide in the presence of antimony pentafluoride SbF5 in solution in SO2ClF. This reaction leads to the formation of a mixture of sec-butyloxocarbonium (74%), tert-butylcarbonium (25%) and tert-butyloxocarbonium (1%) ions.
The problem that the present invention has sought to solve consists in the manufacture of hydrocarbon compounds comprising a 2-methyl-butyryl group and mainly 2-methyl-butyryl fluoride from butane, this process not having the disadvantage of a high cost price of the raw material since butane is extracted directly from the alkanes of petroleum cuts.Initially, the applicant undertook the study of the carbonylation of butane in the presence of different superacid systems in order to determine a system capable of leading, in an efficient and economical manner, to obtaining a hydrocarbon-based compound comprising a 2-methyl-butyryl group. In a second step, the applicant undertook the study of the separation of the compound obtained in order to determine the means capable of ensuring, in the most efficient manner possible, the regeneration of the chosen superacid.

The process according to the invention is therefore defined as a catalytic process for the manufacture of 2-methylbutyryl fluoride from carbon monoxide, hydrogen fluoride and a stream of aliphatic hydrocarbons comprising butane as the main title, characterized by the succession of the following steps (a) introduction of at least one fluid chosen from carbon monoxide and
said stream of hydrocarbons in a reactor in the presence of a superacid
consisting of hydrogen fluoride, SbF5 antimony pentafluoride and
at least one compound chosen from bromine and inorganic bromides or
organic, (b) where appropriate, if it has not already been introduced during step (a),
introduction into the reactor of a fluid chosen from monoxide
carbon and said hydrocarbon stream, under conditions specific to
allow the formation, mainly, of a complex consisting of
2-methyl-butyryl cation and the anion SbF6, (c) conversion of said complex to 2-methyl-butyryl fluoride, (d) separation of 2-methyl-butyryl fluoride,
(e) recovery of the superacid, and
(f) if necessary, adjusting the quantity of hydrogen fluoride to the
constitution of the superacid used in step (a).

Thus the method according to the invention necessarily comprises the four stages designated (a), (c), (d) and (e). In this case the carbon monoxide and the stream comprising the butane as the main title are introduced
simultaneously in the reactor. Alternatively it may not be necessary
re simultaneously bringing the carbon monoxide and the stream comprising the butane as the main title in the presence of the superacid. In this second case, the carbon monoxide and said stream of hydrocarbons will be introduced separately into the reactor by virtue of the additional step (D).

For a good understanding of the invention, it should be specified
that - by "cassock mainly" means that the flow of hydrocarbons ali
phatics may include, besides butane, small proportions of at least
very alkanes, alkenes or alkynes having a low number of carDo atoms
ne, such as in particular ethane or propane, as well as a medium proportion
noritaire of Dutène.

- By "main title 2-methyl butyryl cation" is meant that the reaction
generated by the superacid system essentially leads to the formation
of this cation (also called sec-butyloxocarbonium), next to propor
minorations of carbocations either derived from other flydrocarbons ali
phatics possibly present in the reaction medium either come from
butane enupurP5 and / or the 2-methyl butyryl cation.

- By "inorganic or organic bromide" is meant an ionic compound in the
which at least one bromine atom is linked to a metal atom or else a
organic group; examples of such compounds are in particular brGleu-
alkali and alkaline earth res and quaternary ammonium bromides.

In addition, the content of the description which follows is intended to specify the embodiment of each of the steps of the process.
lon the present invention. The purpose of step (a) is to bring either the mono carbon dioxide, or the flow comprising the propane as the main title, or their mixture, in contact with the superacid system. This bringing together is carried out in a reactor which may be of the autoclave type or else of the tubular type or of any other type suitable for bringing the reagents into contact.

On the other hand, when the said reagent (s) are introduced into the reactor, the latter already contains the superacid system. This comprises hydrogen fluoride, antimony pentafluoride SbF5 and at least one compound chosen from bromine and inorganic or organic bromides in proportions such that they constitute a homogeneous phase.

During step (b), optional as indicated above, the other component is introduced into the reactor. It is only from this moment that, carbon monoxide and butane being in contact with the superacid, a complex consisting of the 2-methyl butyryl cation and the SbF6 anion will begin to form mainly. The presence of said cation is confirmed by sampling the reaction medium at this stage and analysis, in particular by proton nuclear magnetic resonance. By this analysis, a spectrum is obtained comprising a triplet at approximately 1.25 ppm (3H), a doublet at approximately 1.85 ppm (3H), a multiplet at approximately 2.3 ppm (2H) and a sextuplet at 4.15 ppm. ppm (1H). For the formation of said complex to take place as efficiently as possible, it is desirable that the operating conditions in the reactor be chosen as follows - a CO / C4H1o molar ratio of at least 1.5 and preferably understood
between 2 and 30 approximately, - an HF / SbF5 molar ratio of between 1 and 30 approximately, - a temperature between -80 C and +60 "C approximately, - a proportion of bromine or inorganic or organic bromide, relative to
SbF5, between 0.1 and 5 mol% approximately.

The complex formed at the end of step (b) is used, in particular by virtue of the embodiment described below, to produce 2-methyl-butyryl fluoride with a good yield.

According to a first embodiment of the process according to the invention, the complex is converted into 2-methyl-butyryl fluoride by the intervention of at least one means for shifting the equilibrium between said complex and the 2-methyl-butyryl fluoride towards the formation of the latter. Among the means of intervention, in the context of step (c), to displace this chemical equilibrium, mention may in particular be made of the addition of a chemical species capable of significantly reducing the acidity of the reaction medium. Among such species, hydrogen fluoride will preferably be chosen. Means of intervention of a physical nature, for example thermal, can also be envisaged in the context of step (c).

The aforementioned chemical equilibrium having been sufficiently displaced, it is then appropriate in step (d) to separate a substantial proportion of the 2-methyl-butyryl fluoride from the other constituents of the reaction medium.

Knowing the boiling temperatures at atmospheric pressure of hydrogen fluoride (20 "C), antimony pentafluoride (150" C) and 2-methyl-butyryl fluoride, as well as the respective amounts of the various components present , those skilled in the art are able to choose the most suitable separation method.

Still in the context of this embodiment, the process according to the present invention further provides for the superacid and optionally the residual 2-methyl-butyryl fluoride to be recovered during step (e). When the process is carried out batchwise, the superacid, alone or as a mixture with hydrogen fluoride and optionally a part of the 2-methyl-butyryl fluoride which has not been separated, is recovered to be reused for the next reaction. When the process is carried out continuously, the superacid, optionally mixed with hydrogen fluoride and / or 2-methyl-butyryl fluoride, is recycled to the reactor. When hydrogen fluoride has been added during step (c), the recycling can be carried out after partial elimination of the hydrogen fluoride. In this case a particular embodiment consists in adjusting, thanks to step (f), the amount of hydrogen fluoride in the constitution of the superacid used in step (a). The hydrogen fluoride removed at this stage can in turn be recycled, for example to the intervention point of stage (c) or it will at least partially make it possible to constitute the make-up necessary for the displacement of the chemical equilibrium above mentioned.

The reaction of the process according to the present invention can be conveniently carried out under atmospheric pressure. For reasons of kinetics and economy of industrial operation, it may also be advantageous to proceed under a pressure greater than atmospheric pressure, for example under a pressure ranging up to 250 bars. Those skilled in the art are able to choose, as a function of the pressure level, on the one hand the residence time of the reaction medium in the reactor and on the other hand the appropriate temperature. The residence time in the reactor is generally between 0.1 and 300 minutes. In addition, in the case where the reaction pressure is significantly higher than atmospheric pressure, it may be desirable to lower the pressure after the reaction. step (c) and recompress the fluids recovered in particular during step (e) and, where appropriate, during step (f) to the pressure of the reactor.

The process according to the invention makes it possible to obtain with satisfactory kinetics and yield, after at least one purification step well known to those skilled in the art such as fractional distillation, 2-methyl butyryl fluoride having a degree of purity suitable for subsequent uses. In fact, 2-methyl-butyryl fluoride constitutes a synthetic intermediate allowing in particular the production of 2-methyl-butyric acid by hydrolysis. In accordance with the objective of the present invention, this compound is obtained at a moderate cost due to the choice of butane as the starting raw material.

The sole object of the example below is to illustrate the present invention, without limiting its scope in any way.

EXAMPLE
In a polymonochlorotrifluoroethylene reactor with a volume of 3 ml containing a mixture of hydrogen fluoride and antimony pentafluoride in an HF / SbF5 molar ratio equal to 7: 3 as well as sodium bromide at a rate of 2.5% by moles with respect to SDF5, immerse a tube in polymonochlorotrifluoroethylene through which is introduced, at a flow rate of 210 ml / hour, a mixture of carbon monoxide and butane in a molar ratio
CO / C4H10 equal to 3. This reactor is maintained under spherical atmospheric pressure and, thanks to a brine bath, at a temperature of -10 C. The gas circulation is ensured by a peristaltic pump through a circuit made up of tubes in polytetrafluoroethylene. At the outlet of the reactor, a refrigerant enveloping the tube is supplied with ethanol by a cryostat, in order to condense the hydrogen fluoride vapors which could escape from the medium. Downstream of this tube, a polytetrafluoroethylene soda trap trap makes it possible to stop the last traces of hydrogen fluoride.

After 60 minutes of operation, a fraction of the liquid phase is taken from the immersion tube in the reactor with a view to its analysis by proton nuclear magnetic resonance. This analysis allows - on the one hand to determine the conversion rate equal to the proportion of bu
tane consumed relative to the amount of butane introduced. This rate is
here equal to 78%.

- on the other hand, to identify the cations formed during the reaction. The
nuclear magnetic resonance spectrum obtained (already described above)
reveals the presence of 2-methyl butyryl, isobutyryl and propiony cations
the and allows to evaluate their respective proportions:
2-methyl butyryl: 93%
isobutyryl: 3%
propionyl: 4%
These proportions are further confirmed by gas chromatographic analysis after trapping the reaction medium in a mixture of ethanol and sodium bicarbonate.

Claims (12)

1. Catalytic process for the production of 2-methyl butyryl fluoride from carbon monoxide, hydrogen fluoride and a stream of alipnatic hydrocarbons comprising mainly butane, characterized by the succession of the following steps (a ) introduction of at least one fluid chosen from carbon monoxide and said stream of hydrocarbons in a reactor in the presence of a superacid consisting of hydrogen fluoride, SbF5 antimony pentafluoride and at least one compound chosen from bromine and inorganic bromides or organic, (b) where appropriate, if it has not already been introduced during step (a), introduction into the reactor of a fluid chosen from monoxide carbon and said hydrocarbon stream, under conditions specific to allow the formation, mainly, of a complex consisting of cation of 2-methyl butyryl and the anion SbF6, (c) conversion of said complex to 2-methyl-butyryl fluoride, (d) separation of 2-methyl-buturyl fluoride, and (e) recovery of the superacid. 2. Method according to claim 1, characterized in that the CO / C4H10 molar ratio in the reactor is at least equal to 1.5. 3. Method according to one of claims 1 and 2, characterized in that the HF / SbF5 molar ratio in the reactor is between 1 and 30. 4. Method according to one of claims 1 to 3, characterized in that the reaction temperature is between -80 C and +60 "C. 5. Method according to one of claims 1 to 4, characterized in that the proportion of the compound chosen from bromine and inorganic or organic bromides is between 0.1 and 5% by moles relative to SbF5. 6. Method according to one of claims 1 to 5, characterized in that the complex formed at the end of step (b) is converted into 2-methyl butyryl fluoride during step (c) by intervention of at least one means for shifting the equilibrium between said complex and the 2-methyl-butyryl fluoride towards the formation of the latter. 7. The method of claim 6, characterized in that the intervention means of step (c) is the addition of a chemical species capable of significantly reducing the acidity of the reaction medium. 8. Method according to claim 7, characterized in that said chemical species is hydrogen fluoride. 9. Method according to one of claims 1 to 8, characterized in that the superacid recovered during step (e) is recycled to the reactor. 10. The method of claims 8 and 9, characterized in that the recycling of the superacid is carried out after partial removal of hydrogen fluoride. 11. The method of claim 10, characterized in that the hydrogen fluoride removed at this stage is recycled to the intervention point of step (c). 12. Method according to one of claims 10 and 11, characterized in that it further comprises a step (f) of adjusting the amount of hydrogen fluoride to the constitution of the superacid used in 1 step. (at).